Goal:
    _z_ : VSet.t  x0 : V.t  x1 : V.t  x2 : V.t  a : V.t
  ============================
   ((x0 = a \/ x1 = a \/ x2 = a \/ VSet.In a _z_ ->
     x1 = a \/ x2 = a \/ x0 = a \/ VSet.In a _z_) /\
    (x1 = a \/ x2 = a \/ x0 = a \/ VSet.In a _z_ ->
     x0 = a \/ x1 = a \/ x2 = a \/ VSet.In a _z_))


DEBUG:Going to execute:
<Coq.Init.Tauto.is_conj> flags X1; Ltac.split
Level 3: evaluation returns
<coq-core.plugins.tauto::find_cut@0>
where
k := fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]
     where
     flags := 
     of type
     tauto_flags
of type
tacvalue of type tacvalue

Level 3: Backtrace:

Tactic failure: No matching clause.
Level 3: Backtrace:

Tactic failure: No matching clause.
Level 3: Backtrace:

Tactic failure: No matching clause.
Level 2: Backtrace:

Tactic failure: No matching clause.